Electric power generating system for vehicle

ABSTRACT

An electric power generating system for a vehicle includes a generator having a field coil, a voltage regulator, a temperature sensor for sensing temperature of the voltage regulator, a field current restricting circuit that directly restricts field current if temperature of the voltage regulator becomes higher than a maximum level and a device that prevents temperature of the voltage regulator from further rising without directly restricting field current if temperature of the voltage regulator becomes a warning level that is lower than the maximum level.

CROSS REFERENCE TO RELATED APPLICATION

The present application is based on and claims priority from JapanesePatent Application 2004-147095, filed May 18, 2004, the contents ofwhich are incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an electric power generating system tosupply electric power to a battery or various electric loads that is orare mounted in a vehicle.

2. Description of the Related Art

When temperature of a voltage generator that is built in a vehicle'selectric power generator rises up, field current supplied by the voltageregulator to the field coil of the generator is controlled to preventthe temperature from further rising up, as disclosed in JP-A-8-9567 orin JP-B2-3159976.

If the temperature around the voltage regulator rises up, the outputpower of the generator decreases in case the above temperature controlis carried out. This may cause insufficient performance or operation ofthe electric loads such as head lamps.

SUMMARY OF THE INVENTION

The present invention is to provide an improved electric powergenerating system. That is, the improved electric power generatingsystem does not significantly decrease the output power even if theambient temperature of a built-in voltage regulator rises up.

According to an embodiment of the invention, an electric powergenerating system for a vehicle includes a generator having a fieldcoil, a voltage regulator that includes an overheat control circuit forcontrolling field current if temperature of the voltage regulatorbecomes higher than a first threshold value, a temperature sensor thatsenses temperature of the voltage regulator, cooling means for coolingthe voltage regulator and control means for operating the cooling meansif temperature of the voltage regulator becomes higher than a secondthreshold value that is lower than the first threshold value. Therefore,the output power of the generator will not decrease as long as thecontrol means effectively operates the cooling means. In the electricpower generating system as described above the cooling means preferablyincludes a motor-driven cooling fan. The motor-driven cooling fan ispreferably disposed near an engine to also cool engine coolant.

According to another embodiment of the invention, an electric powergenerating system for a vehicle includes a generator having a fieldcoil, a voltage regulator that includes an overheat control circuit thatcontrols field current supplied to the field coil if temperature of thevoltage regulator becomes higher than a first threshold value, atemperature sensor that senses temperature of said voltage regulator,and control means that turns off such electric loads that do not affectvehicle driving conditions if temperature of the voltage regulatorbecomes higher than a second threshold value that is lower than thefirst threshold value. Therefore, the output power of the generator willnot decrease as long as the control means effectively turns off suchelectric loads. In the above-described embodiment, the electric loads tobe turned off may be an audio device or a seat heater.

BRIEF DESCRIPTION OF THE DRAWINGS

Other objects, features and characteristics of the present invention aswell as the functions of related parts of the present invention willbecome clear from a study of the following detailed description, theappended claims and the drawings. In the drawings:

FIG. 1 is a block diagram of an electric power generating systemaccording to the first embodiment of the invention;

FIG. 2 is a flow diagram of operation of the electric power generatingsystem according to the first embodiment of the invention;

FIG. 3 is a block diagram of an electric power generating systemaccording to the second embodiment of the invention; and

FIG. 4 is a flow diagram of operation of the electric power generatingsystem according to the second embodiment of the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Two kinds of electric power generating systems according to preferredembodiments of the present invention will be described with reference tothe appended drawings.

An electric power generating system for a vehicle according to the firstembodiment of the invention will be described with reference to FIGS. 1and 2.

As shown in FIG. 1, the power generating system according to the firstembodiment includes a vehicle's electric power generator (hereinafterreferred to the generator) 1, a voltage regulator 2, an on-vehiclebattery 3, an engine control unit (hereinafter referred to as the ECU)4, an electric load 5, a head lamp 7, etc. The ECU 4 connects to anengine 80 and a motor-driven cooling fan 82 that cools the engine 80.

The generator 1 has a stator core on which three-phase stator winding 11is mounted, a three-phase full-wave rectifying unit 12 and a rotor onwhich a field coil 13 is mounted. The output voltage of the generator 1is controlled by the voltage regulator 2 that switches on or off fieldcurrent supplied to the field coil 13 in a controlled manner. Thegenerator 1 is connected to the battery 3 at its output terminals tocharge the battery 3. The battery 3 connects to the ECU 4, the electricload 5 and the head lamp 7.

The voltage regulator 2 controls the field current supplied to thegenerator so that the output voltage of the generator 1 becomes apredetermined voltage. The voltage regulator 2 includes a controlcircuit 21, power transistor 22, a flywheel diode 23, a temperaturesensor 24, etc. The control circuit 21 turns on or off the powertransistor 22 so that the output voltage of the generator 1 can be thesame voltage level as the predetermined voltage. The control circuit 21includes a temperature detecting circuit 211, an overheat protectingcircuit 212 and a data transmission circuit 213. The control circuit 21detects temperature of the voltage regulator 2, sends temperature datato the ECU 4 and controls the field current according to thetemperature. The temperature detecting circuit 211 detects thetemperature of the voltage regulator 2 with the temperature sensor 24,which is disposed inside the voltage regulator 2. The temperaturedetecting circuit 211 has two output terminals S1, S2 respectivelyconnected to the overheat protecting circuit 212 and the datatransmission circuit 213. If the detected temperature T becomes higherthan a first threshold value T1, the output terminal S1 provides a highlevel signal. If the detected temperature T becomes higher than a secondthreshold value T2 that is lower than the first threshold value, theoutput terminal S2 of the temperature detecting circuit 211 provides ahigh level signal. In other words, if the temperature of the voltageregulator 2 continuously rises up after the generator 1 startsgenerating electric power, the signal of the output terminal S2 changesfrom a low level signal to a high level signal. Then, the signal of theother output terminal S1 changes from a low level signal to a high levelsignal while the output terminal S2 maintains the high level signal.

If the output terminal S1 of the temperature detecting circuit 211provides a high level signal, the overheat protection circuit 212controls or reduces the field current supplied to the field coil 13. Ifthe output terminal S2 of the temperature detecting circuit 211 providesa high level signal, the data transmission circuit 213 sends atemperature rise signal to the ECU 4 via a terminal X. These signals aremaintained continuously or cyclically until the temperature T detectedby the temperature detecting circuit 211 becomes lower than the secondthreshold value T2, and the signal of the output terminal S2 of thetemperature detecting circuit 211 comes back to a low level signal.

The power transistor 22 is connected in series with the field coil 13 ofthe generator 1. The field current is supplied to the field coil 13 whenthe control circuit 21 turns on the power transistor 22. When the fieldcurrent is to be reduced, the overheat protection circuit 212 reducesthe duty ratio of the field current control signal applied to the powertransistor. The flywheel diode 23 is connected in parallel with thefield coil 13 to pass the field current when the power transistor 22 isturned off.

The ECU 4 is an outside unit that controls the operation of the engine80 according to a depressing amount of an accelerator pedal (not shownhere) and operates the motor-driven cooling fan 82 to cool enginecoolant if the temperature of the engine coolant becomes higher than apredetermined value. The ECU 4 also turns on the motor-driven coolingfan 82 when a temperature rise signal is sent from the terminal X of thevoltage regulator 2. The ECU 4 is empowered by the battery 3 like theelectric load 4 and the head lamp 7.

The generator 1 and the voltage regulator 2 are directly fixed to theengine via fixing members. When the motor-driven fan 82 is operated inorder to cool the coolant flowing into the radiator 81, a portion of airthat is introduced to spaces around the engine is further supplied tospaces around the generator 1 and the voltage regulator 2. Thus, themotor-driven fan 82 functions to cool the voltage regulator 2.

The control operation of the electric power generating system accordingto the first embodiment will be described with reference to a flowdiagram shown in FIG. 2.

When the engine 80 starts and the generator 1 and the voltage regulator2 start their operation, the temperature detecting circuit 211 of thecontrol circuit 21, whether the temperature T indicated by thetemperature sensor 24 is higher than the second threshold value T2 ornot is examined at step 100. If the result is NO, the above step isrepeated. If the result is YES, the output terminal S2 of thetemperature detecting circuit 211 provides a high level signal, so thatthe data transmission circuit 213 sends a temperature rise signal to theECU 4 via the terminal X at step 101. When the ECU 4 receives thetemperature rise signal, it operates the motor-driven cooling fan 82 atstep 102. Therefore, outside air is introduced into the spaces aroundthe engine 80 through the radiator 82.

Then, the temperature detecting circuit 211 examines whether thetemperature T returns to a temperature lower than the second thresholdvalue T2 or not at step 103. If the temperature T is still higher thanthe second threshold value T2, NO is provided. Next, the temperaturedetecting circuit 211 further examines whether the temperature T becomeshigher than the first threshold value T1 or not at step 104. If thetemperature T is higher than the second threshold value T2 and lowerthan the first threshold value T1, No is provided and the controloperation goes to step 103.

After the motor-driven cooling fan 82 is operated, the temperature T maygradually drop and become lower than the second threshold value T2. Inthat case, YES is provided at step 103. Then, the data signal that hasbeen sent from the data transmission circuit 213 to the ECU 4 is stoppedat step 105. Accordingly, the ECU 4 stops operation of the motor-drivencooling fan 82 at step 106, and the control operation returns to step100.

If the temperature T rises up to a temperature higher than the firstthreshold value T1 even though the motor-driven cooling fan 82 isoperated, YES is provided at step 104. In that case, the output terminalS1 of the temperature detecting circuit 211 provides a high levelsignal, so that the overheat protection circuit 212 limits the fieldcurrent at step 107. Thereafter, the control operation returns to step104.

Thus, the motor-driven cooling fan 82 is operated before the temperaturebecomes higher than the first threshold value T1 at which the overheatprotection circuit 212 starts to limit the field current. Therefore, theoutput power of the generator does not decrease even if the temperaturegradually rises.

Usually, the generator 1 and the voltage regulator 2 are disposed nearthe engine 80. Therefore, the voltage regulator 2 is effectively cooledwhen the motor-driven cooling 82 takes air into spaces around the engine80 to cool the radiator 81 and the engine 80, thereby reducing radiantheat thereof.

An electric power generating system for a vehicle according to thesecond embodiment of the invention will be described with reference toFIGS. 3 and 4.

As shown in FIG. 3, the power generating system according to the secondembodiment includes a vehicle's electric power generator (hereinafterreferred to the generator) 1, a voltage regulator 2, an on-vehiclebattery 3, an engine control unit (hereinafter referred to as the ECU)4, a first electric load 5, such as an audio device or a seat heater,which does not relate to or affect vehicle driving conditions, a secondelectric load 6, such as a head lamp 7 or the ECU 4, which may affectvehicle driving conditions, etc. Incidentally, the same referencenumeral represents the same or substantially the same part, component orstep as presented in the above description and drawings.

The ECU 4 is different in function from that of the first embodiment.The ECU 4 turns off the second electric load 5 when it receives atemperature rise signal from the voltage regulator 2 and turns on thesecond electric load when it does not receive the temperature risesignal.

A portion of the control operation of the electric power generatingsystem according to the second embodiment that is different from theoperation of the first embodiment will be described with reference to aflow diagram shown in FIG. 4.

When the ECU 4 receives the temperature rise signal from the voltageregulator 2, it sends a stop signal to the first electric load 5 to turnoff at step 102A. The ECU 4 may turn off a switch connected between theelectric load 5 and a power source. When the voltage regulator 2 stopsthe temperature rise signal at step 105, the ECU 4 turns on the electricload 5 at step 106A.

Thus, the field current is reduced without affecting vehicle drivingconditions before the temperature becomes higher than the firstthreshold value T1 at which the overheat protection circuit 212 startsto limit the field current. Therefore, the output power of the generatordoes not decrease even if the ambient temperature gradually rises.

It is possible to employ an additional cooling fan to exclusively coolthe voltage regulator 2 in substantially the same manner as theabove-described motor driven cooling fan 82 for the radiator 81. Thetemperature sensor 24 that is disposed in the voltage regulator 2 can bedisposed outside the voltage regulator 1.

In the foregoing description of the present invention, the invention hasbeen disclosed with reference to specific embodiments thereof. It will,however, be evident that various modifications and changes may be madeto the specific embodiments of the present invention without departingfrom the scope of the invention as set forth in the appended claims.Accordingly, the description of the present invention is to be regardedin an illustrative, rather than a restrictive, sense.

1. An electric power generating system for a vehicle comprising: a generator including a field coil; a voltage regulator for controlling output voltage of said generator, said voltage including an overheat control circuit for controlling field current supplied to the field coil if temperature of said voltage regulator becomes higher than a first threshold value; a temperature sensor for sensing temperature of said voltage regulator; cooling means for cooling said voltage regulator; and control means for operating said cooling means if temperature of said voltage regulator becomes higher than a second threshold value that is lower than the first threshold value.
 2. The electric power generating system as claimed in claim 1, wherein said cooling means comprises a motor-driven cooling fan.
 3. The electric power generating system as claimed in claim 2, wherein said motor-driven cooling fan is disposed near an engine to also cool engine coolant.
 4. An electric power generating system for a vehicle comprising: a generator including a field coil; a voltage regulator for controlling output voltage of said generator, said voltage including an overheat control circuit for controlling field current supplied to the field coil if temperature of said voltage regulator becomes higher than a first threshold value; a temperature sensor for sensing temperature of said voltage regulator; a plurality of electric loads connected to said generator; and control means for turning off a portion of said plurality of electric loads if temperature of said voltage regulator becomes higher than a second threshold value that is lower than the first threshold value.
 5. The electric power generating system as claimed in claim 4, wherein said portion of said plurality of electric loads comprises an electric load that does not directly affect a vehicle driving condition.
 6. The electric power generating system as claimed in claim 5, wherein said portion of said plurality of electric loads comprises one of an audio device and a seat heater.
 7. An electric power generating system for a vehicle comprising: a generator including a field coil; a voltage regulator for controlling output voltage of said generator; a temperature sensor for sensing temperature of said voltage regulator; first means, connected to said voltage regulator and said temperature sensor, for directly restricting field current supplied to the field coil if temperature of said voltage regulator becomes higher than a first threshold value; and second means, connected to said temperature sensor, for preventing temperature of said voltage regulator from further rising without directly restricting field current if temperature of said voltage regulator becomes higher than a second threshold value that is lower than the first threshold value.
 8. The electric power generating system as claimed in claim 7, wherein said second means comprises a motor-driven cooling fan that cools said voltage regulator when the temperature of said voltage regulator becomes higher than the second threshold value.
 9. The electric power generating system as claimed in claim 7, wherein said second means comprises means for turning off an electric load if temperature of said voltage regulator becomes higher than the second threshold value. 